Method and arrangement for controlling moisture in a multiroll calender

Abstract

A method and an arrangement for controlling evaporation and moisture in a multinip calender ( 10 ) when a continuous fibrous web (W) is calendered in calendering nips ( 1, _ 2, — 3, — 4, — 5 ) placed one after the other before the fibrous web is wound on a reel-up/winder ( 9 ). With a view to making the net evaporation from and the final moisture content of the web (W) constant when the running situations in the calender ( 10 ) change, the web is passed in the calender from the outlet of at least one nip into an air-float chamber ( 20 ) of the turning airborne type.

1. A method for controlling evaporation and moisture in a multinip calender when a continuous fibrous web is calendered in a plurality of calendering nips placed one after the other before the fibrous web is wound on a reel-up/winder, comprising the step of passing the web which is calendered from an outlet of at least one nip into an air-float chamber of the turning airborne type, to make the net evaporation from and the final moisture content of the web constant when the running situations in the calender change. 
     
     
       2. The method of  claim 1 , wherein an air-float chamber is arranged in connection with the outlet of several nips of the plurality of calendering nips of the multinip calender. 
     
     
       3. The method of  claim 2 , wherein the multinip calender plurality of nips includes a last nip, and wherein each nip has an associated outlet, and wherein an air-float chamber is arranged in connection with the outlet of each nip of the calender except the last nip of the calender. 
     
     
       4. The method of  claim 1  wherein, the web is moisturized in proportion to the amount of liquid evaporating from the web during calendering in order to prevent large drying/moisturizing cycles. 
     
     
       5. The method of  claim 1 , wherein the web is calendered in at least one calendering nip after the air-float chamber in the glass transition region of the web at a temperature corresponding to at least the glass transition temperature of the web. 
     
     
       6. An arrangement for controlling evaporation and moisture in a multinip calender for the calendering of a continuous fibrous web, the arrangement comprising:
 a plurality of calendering nips placed one after the other, wherein the web passes through each of the plurality of calendering nips;  
 a reel-up/winder which winds the web after it has passed through the plurality of calendering nips; and  
 an air-float chamber of the turning airborne type in connection with the outlet of at least one of the plurality of calendering nips, the web passing through said air-float chamber, the air-float chamber serving to make the net evaporation from and the final moisture content of the web constant when the running situations in the calender change.  
 
     
     
       7. The arrangement of  claim 6 , wherein an air-float chamber is in connection with an outlet of each of several nips of the plurality of calendering nips of the multinip calender. 
     
     
       8. The arrangement of  claim 7 , wherein the plurality of calendering nips includes a last nip, and wherein each nip has an associated outlet, and wherein an air-float chamber is arranged in connection with the outlet of each nip of the calender except the last nip of the calender. 
     
     
       9. The arrangement of  claim 6  wherein the air-float chamber further comprises a moisturizing device, whereby web is moisturized in proportion to the amount of liquid evaporating from the web during calendering, in order to prevent evaporation of moisture and large drying/moisturizing cycles. 
     
     
       10. The arrangement of  claim 6 , wherein, after the air-float chamber, the temperature of the web, when it is calendered, is in the glass transition region of the web in at least one calendering nip, the web being at a temperature corresponding to at least the glass transition temperature of the web when it is calendered. 
     
     
       11. The arrangement of  claim 6 , wherein the air-float chamber includes a closed evaporation control device operating according to a given control. 
     
     
       12. The arrangement of  claim 11  wherein the closed evaporation control device comprises a blow box. 
     
     
       13. The arrangement of  claim 6 , wherein the air-float chamber is closed and comprises two blow boxes spaced from each other such that between the blow boxes there is a passage for the web for turning the running direction of the web. 
     
     
       14. The arrangement of  claim 13 , wherein the air-float chamber comprises, enclosed in a common housing:
 an inner blow box having a surface facing the web which is curved outwards and which is not in contact with the web; and  
 an outer blow box having a surface facing the web which is curved inwards and which is not in contact with the web, wherein the curved surface of the outer blow box substantially corresponds in shape to the curved surface of the inner blow box but has a radius of curvature larger than the radius of curvature of the inner blow box in order to form a passage for the web, which passage extends through the air-float chamber and is not in contact with the web.  
 
     
     
       15. The arrangement of  claim 14 , wherein the feed of a medium, including its feed pressure, feed temperature and feed quantity, into one blow box is independent of the feed of a medium fed into the other blow box, in which connection control or regulation of the temperature, moisture of and evaporation from one side of the web is independent of the moisture, temperature of and evaporation from the other side of the web. 
     
     
       16. The arrangement of  claim 13  wherein the blow boxes are arranged to moisturize the web in a cross direction such that the edge parts of the web can be treated differently from the middle parts of the web, to control moisture of and evaporation from the web in the cross direction with respect to the machine direction of the paper machine. 
     
     
       17. The arrangement of  claim 6 , wherein the web passes through a moisturizing device, and wherein a moisturizing medium in the moisturizing device is air, steam or an equivalent gaseous medium. 
     
     
       18. A papermaking calender apparatus for the calendering of a continuous fibrous web, the apparatus comprising:
 a plurality of calendering nips placed one after the other, wherein the web passes through each of the plurality of calendering nips;  
 an upper roll;  
 a lower roll, wherein the lower roll engages against the upper roll to define one of said plurality of calendering nips;  
 a reel-up/winder which winds the web after it has passed through the plurality of calendering nips; and  
 an air-float chamber of the turning airborne type in connection with the outlet of said one of said plurality of calendering nips, the web passing through said air-float chamber, the air-float chamber affecting the net evaporation from and the final moisture content of the web.  
 
     
     
       19. The papermaking calender apparatus of  claim 18 , wherein the air-float chamber comprises, enclosed in a common housing:
 an inner blow box having a surface facing the web which is curved outwards and which is not in contact with the web; and  
 an outer blow box having a surface facing the web which is curved inwards and which is not in contact with the web, wherein the curved surface of the outer blow box substantially corresponds in shape to the curved surface of the inner blow box but has a radius of curvature larger than the radius of curvature of the inner blow box in order to form a passage for the web, which passage extends through the air-float chamber and is not in contact with the web.  
 
     
     
       20. The papermaking calender apparatus of  claim 19 , wherein the feed of a medium, including its feed pressure, feed temperature and feed quantity, into one blow box is independent of the feed of a medium fed into the other blow box, in which connection control or regulation of the temperature, moisture of and evaporation from one side of the web is independent of the moisture, temperature of and evaporation from the other side of the web.